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MICS Results
Surgically Induced Astigmatism & MICS
The optical quality of the cornea plays an important role in recovery of visual function after cataract surgery, and this is determined by combination of corneal and internal aberrations generated by the IOL and those induced by the surgery. These corneal refractive changes are attributed to the location and size of the corneal incision. The smaller incision, lower aberrations means better optical quality. Degraded optical quality of the cornea after incisional cataract surgery would limit the performance of the pseudophakic eye. Thus, it is important not to increase or to induce astigmatism and/or corneal aberrations after cataract surgery.
Symmetrically placed two small incisions give MICS an advantage over rest of the cataract surgery techniques because 1.5 mm incision is practically neutral for corneal biomechanics. Even with MICS, it is possible to achieve reduction of the astigmatism and higher-order corneal aberrations if the incisions are placed on place corresponding to the main axis of astigmatism.
Great advantage of MICS is the reduction of SIA and that the microincisions do not produce an increase in astigmatism when compared with conventional 3 mm phacoemulsification (Figure 1). The shorter the incision, the less the corneal astigmatism, as it was estimated that the magnitude of the SIA studied by vector analysis was around 0.44 and 0.88 D, rising as the size of the incision increased. This is considered important because cataract surgery today is considered more and more a refractive procedure. Also, small-incision surgery (3.5-mm incision without suture) does not systematically degrade the optical quality of the anterior corneal surface. However, it introduces changes in some aberrations, especially in no rotationally symmetric terms such as astigmatism, coma and trefoil. Therefore, one has to expect better results and lesser changes with sub 2 mm incision (MICS). This is supported by the finding that the corneal incision of <2 mm had no impact on corneal curvature. It is important to go hand in hand with the modern concept of making cataract surgery a refractive procedure, by controlling and even decreasing astigmatism and higher-order aberrations (HOAs) by using MICS. MICS sub 2 mm incision effectively decreases the induction or changes in corneal SIA during cataract surgery (Figure 12).
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Figure 12.
Comparison of microincision cataract surgery and coaxial vectoral astigmatic change.
Dick in his study confirms better clinical outcomes of MICS versus coaxial group. MICS group patients showed earlier improvement in BCVA and less SIA. Comparative study of Can et al. also supports less SIA production by MICS. Wilczynski et al. did not notice statistically significant difference in SIA production in both the compared groups. Kaufman et al. did not noticed any statistical difference in keratometry between pre- and postsurgery topographic examination (Table 7).
Corneal Aberration With MICS
A demand for the cataract surgery obliges to not only removal of cataract nucleus but also to improve optical quality of the eye. Market for intraocular lenses gives us opportunity to implant perfect lenses which can diminish total HOAs of the eye. The final visual function is determined by the aberrations produced by the implanted intraocular lens and corneal aberrations changed by the postsurgical incisions. Therefore, the best quality of lenses for cataract surgery should be suggested in order to improve patient's visual outcome.
Elkady et al. and Alió et al. in their prospective cumulative interventional non-randomized, non-comparative study of 25 eyes of 25 patients showed that after the MICS incision smaller than 1.8 mm, there was no statistical difference in corneal power, corneal astigmatism before and 3 months of follow-up after surgery. The RMS value of the total corneal aberrations decreased slightly after MICS (mean 2.15 ± 2.51 µm preoperatively, 1.87 ± 1.87 µm at 1 month and 1.96 ± 2.01 µm at 3 months); there was no statistically significant difference between the two follow-up visits (both p = 1.00, Bonferroni). Analysis of individual Zernike terms showed a mean astigmatism of 0.85 ± 0.74 µm preoperatively, 0.65 ± 0.44 µm at 1 month and 0.69 ± 0.46 µm at 3 months and a mean spherical aberration of -0.11 ± 0.25 µm, -0.09 ± 0.25 µm and -0.19 ± 0.13 µm, respectively. Coma decreased (mean 0.45 ± 0.40 µm preoperatively, 0.39 ± 0.36 µm at 1 month and 0.42 ± 0.44 µm at 3 months, respectively); there was no statistically significant difference between the two follow-up visits (both p = 1.00, Bonferroni). The mean HOA was 0.47 ± 0.26 µm preoperatively, 0.59 ± 0.32 µm at 1 month and 0.54 ± 0.25 µm at 3 months; there was no statistically significant difference between the two follow-up visits (both p > 0.47, Bonferroni).
All aberration values except HOA decreased slightly, with no statistically significant differences between the follow-up visits. All aberration values were stable for 3 months after surgery, indicating that successful MICS depends on preventing induction of HOAs as well as a surgically neutral and stable procedure. Successful MICS gives visual quality equal to that in persons of the same age without pathology and leads to good patient satisfaction (Figure 3).
Denoyer et al. compared MICS with conventional coaxial surgery. This study showed that MICS could improve the optical performances of the pseudophakic eye reducing in 3 months surgically induced corneal HOAs. The postoperative root mean square of 3rd to 6th was lower in MICS group 0.705 ± 0.285 versus 0.956 ± 0.236 µm in coaxial group and it was significantly different (p < 0.001) and the root mean square for the 3rd to 6th order ocular aberration was lower in MICS 0.308 ± 0.122 µm versus coaxial group 0.488 ± 0.172 µm with significant difference (p = 0.002).
Can et al. compared MICS with Co-MICS. They found that only MICS group did not alter corneal aberrations after the surgery, which confirm aberration neutrality of MICS surgery. Tong et al. in a group of 80 patients proved less cataract surgery-related changes in corneal wavefront aberrations after MICS than after coaxial surgery. Coaxial group had greater changes in oblique astigmatism, trefoil, vertical tetrafoil, RMS and higher-order RMS of corneal wavefront.
New comparative study done by Alió et al. of the corneal aberrations after MICS and 2.2 mm coaxial surgery showed that 2 mm incision was the safe limit of the corneal degradation. MICS significantly produced less changes in coma and higher-order aberrations compared with coaxial phaco (Table 8 & Figure 13).
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Figure 13.
Corneal topography maps (axial maps) preoperative versus 1 month after surgery for one eye from each group of the study. Bottom: Corneal aberrometry maps (Seidel panel) preoperative versus 1 month after surgery of the same eyes.
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